1. Field of the Invention
The present invention relates to an apparatus for processing an image of an original, such as copying machines, facsimiles, image memory systems and the like.
2. Description of the Prior Art
In image processing systems, various detections, for example, detection of the size of an original, or detection of the position of an original are carried out. In an image processing system of a type in which an original is carried across the optical path of an image projection optical system by the use of an original conveying device such as a belt or roller while scanning the original, or in which the original is carried to and positioned in a predetermined area on an original supporting surface by the above original conveying device before the image of the original is projected, it is required to detect whether or not the original is in a predetermined position in said optical path, whether or not the original is present on the original supporting surface at a predetermined position or whether or not the original has reached these predetermined positions.
In a further image processing system of a type in which the size of recording paper is selected in response to the detection of the size of original, and in which the projection magnification of an image is automatically changed in response to the combination of the size of original and the size of recording paper or an original is read by an image pick-up element with the resulting data being converted into electrical signals which are used to write the image on a photosensitive surface, a recording paper or the like, the image signals are written only in the region corresponding to the size of original.
The simplest and most practical method for recognizing the position, presence or size of an original is an optical system wherein a region at which an original is set is illuminated, and the resulting reflected light is received by a photosensor, whereafter the output of the photosensor indicative of the intensity of the received light is used to discriminate the position, presence or size of the original.
The region in which an original is placed when the position, presence or size thereof is detected, is usually coincident with a region on which the original is placed for projecting the image thereof onto an electrophotographic type photosensitive member or an image pick-up element. It is usual to locate a covering member in such a region on the side of the backface of the original for placing the original in close contact with the original supporting surface and/or for preventing the original illuminating light from leaking to the outside. The surface of the covering member facing the back side of the original may be recorded as an image if the size of the original is smaller, so that that surface of the covering is generally of a white-colored light diffusion face. On the other hand, the background of the original is often white. It is therefore difficult to discriminate the reflective light from the original from the reflective light of the covering surface on the basis of the output signals of the photosensor.
It has been proposed that the covering surface be colored black or that the covering member be opened if it is desired to detect the position, presence or size of the original. By doing so, identification of the original can easily be made since the photosensor does not receive any light from the region outside of the original. In such a case, however, there is the following problem. Generally, when the image of an original is projected onto a photosensitive member or is read by an image pick-up element, the original is irradiated by illumination means with the resulting reflective light being imaged on the photosensitive member, solid-state image pick-up element or the like through an optical system. At this time, a portion of the light illuminating the original is scatteredly reflected by the surface of the original, while the rest of the light transmitted by the original and exits from the backface of the same. The ratio of these light portions depends on the characteristics of the original such as material, thickness and others. If other paper or a white-colored covering member is behind the original, the light transmitted through the original is reflected by the surface of the other paper or white-colored covering, and again passes through the original and then projected on the photosensitive member or image pick-up element through the above optical system. That is, it is added to the previously projected or read light. In the ordinary image processing systems, accordingly, the level of the white background is determined by the light amount added by the light that has returned through the original. Therefore, if the covering member is black-colored or opened, the light transmitted by the original will be absorbed by the black-colored face of the covering member or scattered into the atmosphere so that such light cannot be used to expose the photosensitive member or to read the image. It follows that the black-colored or opened covering results in reduced level of light amount of the background of the original in comparison with the white-colored covering. For example, in the case of an original made of high-quality paper such as is used in ordinary office work, the reproduced image will have a very foggy background. In the case of an original made of tracing paper such as is generally used in drawing etc., the reproduced image will have dark background so that the information of the image cannot be discriminated from the background.
The currently practical method is that the covering member is colored with the color to which the photosensitive member or image pick-up element is highly sensitive, that is, which is deemed to be white by the photosensitive member or image pick-up element, while using a photosensor which is substantially insensitive to that color. In such a case, the photosensor is less sensitive to the color of the covering member so that it can be discriminated from the white-colored background of the original. However, the color of the original background is not necessarily white. There may be used also any colored background in an original. This method is not applicable to such a case. Further, this method cannot be utilized in a system that uses same element as a photosensor for detecting the position, presence or size of an original and also as an image pick-up element for reading the image of the original to produce electric signals representing the image.